Soft error and transient error detection device and methods therefor

ABSTRACT

A clock signal is received at a clock node of a latch module, and a data signal is received at a data node of the latch module. The data signal including information to be latched at a first latch of the latch module and at a second latch of the latch module. A first representation of the data signal to a first data node of the first latch is delayed relative to a second representation of the data signal to a corresponding first data node of the second latch to obtain a first timing requirement between the data signal and the clock signal relative to the first latch that is substantially different than a second timing requirement. An error signal is generated in response to different data being latched at the first latch than at the second latch.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to data processing devices, andmore particularly, to error detection at data processing devices.

2. Description of the Related Art

Advancements in the performance and computational capabilities ofintegrated circuit (IC) data processing devices are often the result ofa corresponding reduction in the size of the transistors, conductors,and other components that make up the devices. Furthermore, theoperating voltage of modern IC data processing devices is typicallyminimized to increase the operating frequency and to reduce powerdissipation of the devices. Because of these changes, conductors andstorage nodes included at the data processing device havecorrespondingly low capacitance, and therefore are capable of storingonly a small amount of energy. Thus, the device is increasinglysusceptible to soft errors. A soft error can result from the interactionof an energetic neutron or alpha particle with the small conductors andcharge storage nodes of a data processing device. Neutrons typicallyoriginate from cosmic rays, and alpha particles originate from materialspresent in the integrated circuit package and bonding materials.

A combination of the capacitance and the voltage at a node of a deviceis described by a critical charge parameter, Qcrit, which is the minimumelectron charge disturbance needed to change the logic level at thenode. Larger Qcrit values are associated with fewer soft errors.Unfortunately, signals at a node with a larger Qcrit value willtransition slower and dissipate more power than a node with a relativelysmaller Qcrit value. Reduction in the feature size of transistor andconductors at the data processing device and a reduction in theoperating voltage decreases Qcrit. Thus, the incidence of soft errorsincreases as chip technology advances. In a logic circuit, Qcrit isdefined as the minimum amount of induced charge required at a circuitnode to cause a voltage pulse to propagate from that node to the outputof a corresponding logic gate, and be of sufficient duration andmagnitude for an error to be subsequently stored at a down-stream latchdevice. Error correction codes and associated circuitry can be used todetect and sometimes correct soft errors, but is not practical for useat the large number of latches that make up computational logic blocksof a data processing device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 is a block diagram illustrating a data processing deviceincluding a latch capable of detecting a soft error in accordance with aspecific embodiment of the present disclosure.

FIG. 2 is a block diagram illustrating an error-detecting latch of FIG.1 in accordance with a specific embodiment of the present disclosure.

FIG. 3 is a schematic diagram illustrating logic gates and theerror-detecting latch of FIG. 1 in accordance with a specific embodimentof the present disclosure.

FIG. 4 is a timing diagram illustrating the operation of a synchronouslogic circuit of FIG. 1 in accordance with a specific embodiment of thepresent disclosure.

FIG. 5 is a timing diagram illustrating the operation of the synchronouslogic circuit of FIG. 1 in response to a soft error event in accordancewith a specific embodiment of the present disclosure.

FIG. 6 is a schematic diagram illustrating an error-detecting latch,such as the error-detecting latch of FIG. 1 in accordance with aspecific embodiment of the present disclosure.

FIG. 7 is a timing diagram illustrating the operation of the errordetecting latch of FIG. 6 in accordance with a specific embodiment ofthe present disclosure.

DETAILED DESCRIPTION

The present disclosure provides a storage element, such as a latch,operable to detect a soft error or error caused by transientinterference upstream from the latch, and to provide a signal indicativeof the error. The storage element includes multiple latches that receivesubstantially the same clock signal, such that operation of the storageelement is dependent only upon the propagation delay of a singleexternal clock signal. Delays associated with the data paths of themultiple latches are different to facilitate different setup time andhold times at each latch to detect an error event, such as a soft error.

FIG. 1 is a block diagram illustrating a data processing device 100including a synchronous logic circuit 105 that includes latch 110, logicgates 120, and a storage element, also referred to as error-detectinglatch 130. Latch 110 has an input D connected to a node labeled “INPUT,”an input CLK connected to a node labeled “CLOCK,” and an output Qconnected to a node labeled “A.” A logic gate 120 has an input connectednode A and an output connected to a node labeled “Z.” Latch 130 is anerror-detecting latch capable of detecting a soft error in accordancewith a specific embodiment of the present disclosure. Latch 130 has adata input D connected to node Z, a clock input CLK connected to nodeCLOCK, a data output Q connected to a node labeled “OUTPUT,” and anerror detect output E connected to a node labeled “ERROR.”

Logic gates 120 represent what is commonly referred to as “a cloud oflogic” with one or more data inputs and one or more data outputs. Asingle data input, connected to node A, and a single data output,connected to node Z, are illustrated for clarity. A logic gate 120includes logic gates configured to implement a desired logic function. Asignal received at an input of logic gates 120, such as from node A, isdispatched in response to a particular transition of clock signal CLOCK,and the data at the outputs of logic gates 120 are latched on the nextsuch clock transition at a latch, such as error-detecting latch 130.

Error-detecting latch 130 is configured to indicate an error in responseto storage nodes at error-detecting latch 130 latching different data.For purposes of illustration herein it is assumed that a soft error isbeing detected. A soft error can occur when a neutron, an alphaparticle, or other ionizing radiation interacts with synchronous logiccircuit 105 in a manner that causes the logic state of the storage nodeto be altered. For example, the interaction of such a particle canresult in a temporary anomalous transition of a node at logic gates 120that can propagate downstream through one or more logic gates and canresult in an incorrect logic value being stored at a latch device. Ineither case, the particle or radiation results in a soft error event,and the soft error event has an associated duration. Error-detectinglatch 130 includes two or more latches, and data received at a storagenode of each latch is latched in response to a common transition of theclock signal at the input of error-detecting latch 130, such as inresponse to a clock signal transition from a low logic state to a highlogic state. The propagation of the data signal from the data input ofthe error-detecting latch is varied to adjust the setup time and holdtime of each latch so that a soft error event with a duration of lessthan a predetermined period is rejected by at least one of the latches,while the clock signal received at each latch of error detecting latch130 at substantially the same time. Due to variances in conductors usedto propagate signal CLOCK, such as asymmetries in the topology ofconductors used to propagate signal CLOCK, a common transition of theclock signal may begin at one latch associated with error detectinglatch 130 delayed with respect to when it begins at another latch oferror detecting latch 130. The arrival of the clock signal at eachrespective latch is considered to be substantially the same to theextent these variances are not intended to delay one clock transitionfrom another. In a specific embodiment, the arrival of the clock signalat each respective latch is considered to be substantially the same whenthey differ by less than ten picoseconds, less than eight picoseconds,less than 6 picoseconds, or less than four picoseconds, and dependent onthe process technology in which the device is fabricated, e.g. aforty-five nanometer technology.

FIG. 2 is a block diagram illustrating an error-detecting latch 130 ofFIG. 1 in accordance with a specific embodiment of the presentdisclosure. Error-detecting latch 130 includes latch 1302, latch 1304,and error detector 1306. Latch 1302 has a data input D connected toinput D of error-detecting latch 130, a clock input CLK connect to inputCLK of error-detecting latch 130, and an output Q connected to a nodelabeled “Q2.” Latch 1304 has a data input D also connected to node D oferror-detecting latch 130, a clock input CLK also connected to node CLKof error-detecting latch 130, and an output Q connected to a nodelabeled “Q.” Error detector 1306 has an input connected to node Q,another input connected to node Q2, and an output connected to node E.

The setup time (t_(su)) between the data signal received at input D oferror-detecting latch 130 and the clock signal received at input CLK oferror-detecting latch 130 relative to latch 1302 is configured to beequal to S picoseconds (pS), and the hold time (t_(h)) is configured tobe equal to be H pS. The setup time between the data signal received atinput D of error-detecting latch 130 and the clock signal received atinput CLK of error-detecting latch 130 relative to latch 1304 isconfigured to be equal to S+E pS, and the hold time (t_(h)) isconfigured to be equal to H−E pS, where the value E corresponds to adelay to facilitate detection of a soft error. For example, E cancorrespond to a portion of the approximate duration of an expected softerror event, or in the case of a soft error event propagated by logicgates, a portion of the increase in the effective propagation delay of alogic path due to an error event at a node associated with the logicpath. The value of E can be selected to correspond to a soft error eventwith a specific maximum duration. The latching of data at latch 1302 andlatch 1304 is initiated at the same time by clock signal CLOCK receivedat node CLK. The operation of error-detecting latch 130 is described indetail with regard to FIGS. 4-6.

FIG. 3 is a schematic diagram illustrating logic gates 120 anderror-detecting latch 130 of FIG. 1 in accordance with a specificembodiment of the present disclosure. A logic gate 120 includes inverter310, NOR gate 312, NAND gate 314, inverter 316, NAND gate 318, andinverter 320, which are referred to collectively as logic gates 310-320.Inverter 310 has an input connected to node A and an output connected tonode labeled “G.” NOR gate 312 has an input connected to node G, aninput connected to a node labeled “B,” and an output connected to a nodelabeled “H.” NAND gate 314 has an input connected to node H, an inputconnected to a node labeled “C,” and an output connected to a nodelabeled “I.” Inverter 316 has an input connected to node I, and anoutput connected to a node labeled “K.” NAND gate 318 has an inputconnected to node J, an input connected to a node labeled “K,” and anoutput connected to node Z. Inverter 320 has an input connected to anode labeled “D,” and an output connected to node K. Error-detectinglatch 130 has a data input connected to node Z, a clock input connectedto node CLOCK, an error detect output connected to node ERROR, and adata output connected to node OUTPUT.

Logic gates 310-320 represent a generalized configuration ofcombinatorial logic gates that may precede a latch at a synchronouslogic circuit. A signal received at node A can propagate downstream tonodes G, H, I, J, and Z when the logic path is enabled by appropriatelogic values at nodes B, C, and D. Each respective logic gate has acorresponding propagation delay based predominately on the size oftransistors included at that gate, and on the capacitance associatedwith the output node that the gate controls. In order for thesynchronous logic circuit to function correctly, information mustpropagate to node Z before the information is latched at error-detectinglatch 130. Specifically, data provided from node Z to input D must bevalid for a period of time equal to or greater than the setup time oferror-detecting latch 130. In this particular example, the setup time isspecified relative to the rising transition of clock signal CLOCK aninput CLK.

Error-detecting latch 130 is configured to store information received atinput D in response to clock signal CLOCK, and to provide signal ERRORwhen a soft error results in invalid information stored at one of thelatches included at error-detecting latch 130. It is statisticallyunlikely for a soft error event to be of sufficient duration, or for twoindependent soft errors to occur during the same clock cycle, so thatboth latches included at error-detecting latch 130 stores the invalidinformation.

FIG. 4 is a timing diagram 400 illustrating the operation of synchronouslogic circuit 105 of FIG. 1 in accordance with a specific embodiment ofthe present disclosure. Timing diagram 400 includes a horizontal axisrepresenting time in picoseconds (pS), and a vertical axis representingvoltage in volts. Timing diagram 400 includes waveforms 410, 430, 440,450, 460, 470, 480, and 499 representing signals at nodes associatedwith logic gates 120 at FIG. 3. Waveform 410 corresponds to clock signalCLOCK at node CLOCK. Waveform 430 represents a signal at node A,waveform 440 represents a signal at node G, waveform 450 represents asignal at node H, waveform 460 represents a signal at node I, waveform470 represents a signal at node J, waveform 480 represents a signal atnode Z, and waveform 499 represents a signal at node ERROR. Alsoillustrated are time reference T1 492 and time reference T2 494.

Timing diagram 400 illustrates the operation of synchronous logiccircuit 105 in the absence of a soft error event. In response to arising transition of clock signal CLOCK, latch 110 at FIG. 1 begins todrive node A to a logic-high level. Once node A reaches a suitablelevel, inverter 310 begins to drive node G to a logic-low level.Information continues to propagate downstream successively to nodes H,I, J, and ultimately node Z, which is driven to a logic-low level justprior to time reference T1. Time reference T1 492 and time reference T2494 represent the setup times of the two latches included aterror-detecting latch 130, respectively. In the absence of a soft errorevent, valid information (a logic-low value) is successfully stored atboth latches. Thus, signal ERROR is not asserted by error-detectinglatch 130, and waveform 499 remains at a logic-low level.

FIG. 5 is a timing diagram 500 illustrating the operation of synchronouslogic circuit 105 of FIG. 1 in response to a soft error event inaccordance with a specific embodiment of the present disclosure. Timingdiagram 500 includes a horizontal axis representing time in picoseconds(pS), and a vertical axis representing voltage in volts. Timing diagram500 includes waveform 510, 530, 540, 550, 560, 570, 580, and 599representing signals at nodes associated with logic gates 120 at FIG. 3.Waveform 510 corresponds to clock signal CLOCK at node CLOCK. Waveform530 represents a signal at node A, waveform 540 represents a signal atnode G, waveform 550 represents a signal at node H, waveform 560represents a signal at node I, waveform 570 represents a signal at nodeJ, waveform 580 represents a signal at node Z, and waveform 599represents a signal at node ERROR. Also illustrated is time reference T1592, time reference T2 594, time reference TE 542, time reference TR544, interval 546, and interval 548.

In response to a rising transition of clock signal CLOCK at T0, latch110 at FIG. 1 begins to drive node A to a logic-high level. Once node Areaches a suitable level, inverter 310 begins to drive node G to alogic-low level. At approximately time reference TE, a soft error occursat node G. The soft error has a duration that is approximately equal tointerval 544, during which time spurious charge is applied to node Gcausing the voltage at node G to rise to a logic-high level, forexample. It will be appreciated that a soft error need not fullydischarge or charge a node to an anomalous level for the soft error toresult in invalid information being stored at a downstream latch. Merelydelaying the propagation of valid information can cause an error atsynchronous logic circuit 105 to occur. During interval 546, inverter310 continues to drive node G low, which recovers to the logic-low levelat time reference TR 544.

NOR gate 312 responds to the anomalous signal at its input connected tonode G, which is reflected at its output at node H, and to a lesserextent at node I. The affect of the soft error event is not immediatelyevident by the shape of waveform 570, node J, or waveform 580, node Z,but a final signal transition at these nodes is delayed relative towaveforms 470 and 480, respectively, at FIG. 4, as a result of the softerror event. Furthermore, signal 580 is at a logic-high level at timereference T1 592, and at a logic-low level at time reference T2 594.Thus, the two latches included at error-detecting latch 130 containconflicting information, resulting in the assertion of signal ERROR aterror-detecting latch 130, as illustrated by waveform 599. Timingdiagram 500 illustrates a soft error event associated with node G. Itwill be appreciated that error detecting latch 130 is operable to detecta soft error event at any node associated with logic cloud 120, such asnodes A, B, C, D, G, H, I, J, K, and Z.

FIG. 6 is a schematic diagram illustrating an error-detecting latch 600,such as error-detecting latch 130 of FIG. 1, in accordance with aspecific embodiment of the present disclosure. Error-detecting latch 600is a latch module that includes latch 1302, latch 1304, and errordetector 1306. Error-detecting latch 600 has a data input connected tonode D, a clock input connected to node CLK, a data output connected tonode Q, and an error output connected to node ERROR. A data value atdata output node Q is determined based upon a state of latch 1304, andan error indicator at error output node ERROR is based upon the state oflatch 1304 and a state of latch 1302.

Latch 1302 includes inverters 602, 608, 612, 618, and 622, tri-stateinverters 610 and 620, n-channel metal oxide semiconductor (NMOS) fieldeffect transistors 604 and 614, and p-channel metal oxide semiconductor(PMOS) field effect transistors 606 and 616. Inverter 602 has an inputconnected to input node D to receive a data signal and an outputconnected to a data node labeled “D1.” NMOS transistor 604 has a firstcurrent electrode connected to node D1, a control electrode connected toa node labeled “XCLK,” and a second current electrode connected to adata node labeled “SN1.” PMOS transistor 606 has a first currentelectrode connected to node D1, a control electrode connected to nodeCLK, and a second current electrode connected to node SN1. NMOStransistor 604 and PMOS transistor 606 together implement a pass gate.Inverter 608 has an input connected to node SN1 and an output connectedto a data node that includes the input of inverter 612 and the input oftri-state inverter 610. Tri-state inverter 610 has active-high driveenable input connected to node CLK, and an active-low drive enable inputconnected to node XCLK, and an output connected to node SN1.

Inverter 612 has an output connected to a data node that includes firstcurrent electrode of NMOS transistor 614 and a first current electrodeof PMOS transistor 616. NMOS transistor 614 has a control electrodeconnected to clock node CLK, and a second current electrode connected tothe data node that includes the input of inverter 618 and inverter 622,and the output of tri-state inverter 620. PMOS transistor 616 has acontrol electrode connected to node XCLK, and a second current electrodeconnected to the input of inverter 618 and inverter 622, and the outputof tri-state inverter 620. Inverter 618 has an output connected to theinput of tri-state inverter 620. Tri-state inverter 620 has active-highdrive enable input connected to node XCLK, and an active-low driveenable input connected to node CLK. Inverter 622 has an output connectedto a node labeled “Q1,” and to an input of an exclusive-OR gate 624 oferror detector 1306. Inverter 660 has in input connected to node CLK,and an output connected to node XCLK. Exclusive-OR gate 624 has anoutput connected to node ERROR.

Latch 1304 includes inverters 632, 638, 642, 648, and 652, tri-stateinverters 640 and 650, n-channel metal oxide semiconductor (NMOS) fieldeffect transistors 634 and 644, and p-channel metal oxide semiconductor(PMOS) field effect transistors 636 and 646. Inverter 632 has an inputconnected to input node D to receive a data signal and an outputconnected to a data node labeled “D2.” NMOS transistor 634 has a firstcurrent electrode connected to node D2, a control electrode connected tonode XCLK, and a second current electrode connected to a data nodelabeled “SN2.” PMOS transistor 636 has a first current electrodeconnected to node D2, a control electrode connected to node CLK, and asecond current electrode connected to node SN2. Inverter 638 has aninput connected to node SN2 and an output connected to the input ofinverter 642 and to the input of tri-state inverter 640. Tri-stateinverter 640 has active-high drive enable input connected to node CLK,and an active-low drive enable input connected to node XCLK, and anoutput connected to node SN2.

Inverter 642 has an output connected to a data node than includes afirst current electrode (source/drain) of NMOS transistor 644 and afirst current electrode of PMOS transistor 646. NMOS transistor 644 hasa control electrode connected to clock node CLK, and a second currentelectrode connected to the data node that includes the input of inverter648 and inverter 652, and the output of tri-state inverter 650. PMOStransistor 646 has a control electrode connected to node XCLK, and asecond current electrode connected to the input of inverter 648 andinverter 652, and the output of tri-state inverter 650. Inverter 648 hasan output connected to the input of tri-state inverter 650. Tri-stateinverter 650 has active-high drive enable input connected to node XCLK,and an active-low drive enable input connected to node CLK. Inverter 652has an output connected to node Q, and to another input of exclusive-ORgate 624 of error detector 1306.

Latch 1302 is configured to store information received at node D andprovide the stored information at node Q1. Latch 1302 is referred to asa master-slave latch, and includes a master latch provided by inverter608 and tri-state inverter 610, and a slave latch provided by inverter618 and tri-state inverter 620. The master latch is updated while clocksignal CLK is negated. The input of the slave latch is connected to theoutput of the master latch and is updated while clock signal CLK isasserted.

A data signal received at node D is buffered by inverter 602, and isconducted to storage node SN1 by NMOS transistor 604 and PMOS transistor606 while clock signal XCLK is asserted. The output of tri-stateinverter 610 is maintained at a high-impedance state while clock signalXCLK is asserted. When clock signal XCLK is negated (and clock signalCLK is asserted), storage node SN1 is isolated from the output ofinverter 602, and the output of tri-state inverter 610 is enabled todrive storage node SN1. Also in response to the assertion of clocksignal CLK, the slave latch is updated and the stored information isprovided at node Q1.

The operation of latch 1304 is the same as described with reference tolatch 1302. Node Q at the output of latch 1304 is the primary dataoutput of error-detecting latch 130. Exclusive-OR gate 624 compares theinformation stored at latch 1302 and latch 1304, and asserts signalERROR if the value stored at each of the two latches is not the same,such as described with reference to the timing diagram of FIG. 5. Thesetup time and hold time of the master portion of latch 1302 isconfigured to be different than corresponding timing requirements of themaster portion of latch 1304, as described with reference to FIG. 2. Forexample, in an embodiment, the setup time associated with latch 1304 canbe configured to be greater than the setup time associated with latch1302 by an amount greater than approximately one half of the duration ofan anticipated soft error event, such as approximately one-half of asoft error event.

The timing requirements, such as the setup time and hold times inparticular, of the master latches of error-detecting latch 1302 can beset by a combination of circuit attributes that affect the delay of dataalong the data paths that include the master latches. For exampleattributes associated with respective portions 670, 672, 674 and 676 oflatch 1302, and portions 680, 682, 684, and 686 of latch 1304. Portion670 includes inverter 602, portion 672 include NMOS transistor 604 andPMOS transistor 606, portion 674 includes storage node SN1, and portion676 includes inverter 608 and tri-state inverter 610. Portion 680includes inverter 632, portion 682 include NMOS transistor 634 and PMOStransistor 636, portion 684 includes storage node SN2, and portion 686includes inverter 638 and tri-state inverter 640. The setup time andhold time associated with the master latches can be configured by addingdelay elements, adjusting the widths and lengths of individualtransistors, adjusting the threshold voltage of these transistors, andadjusting the capacitance at nodes associated with these transistors.

The setup time and hold time of a latch are examples of timingrequirements that relate the transition of a data signal received at theinput D of the latch 600 to a transition of clock signal at input CLK. Asetup timing requirement specifies a minimum time that a data signalmust be at a valid level prior to an active transition of signal CLK. Ahold timing requirement specifies a minimum time that a data signal mustremain at the valid level following the active transition of signal CLK.Setup and hold times can be positive or negative values. The setup andhold times of latch 1302 (e.g., the timing requirement between the datasignal at input D and the clock signal at input CLK for latch 1302) andlatch 1304 (e.g., the timing requirement between the data signal atinput D and the clock signal at input CLK for latch 1304) are configuredto be substantially different. For example, the data signal along thedata path of latch 1302 can be adjusted, relative to the data signalalong the data path of latch 1304, by an amount that is greater than anexpected variation between the clock paths of latch 1302 and 1304. Forexample, the delay of a data signal can be greater than sixteenpicoseconds. In contrast to the master portions of the latches 1302 and1304, the slave portion of each latch is designed to be substantiallysimilar. For example, inverters 612, 618, 622, NMOS transistor 614, PMOStransistor 616, and tri-state inverter 620 of latch 1302 and theirinterconnects can be designed to have substantially the same electricalproperties as the corresponding devices at latch 1304. Thus, the slaveportion of latch 1302 and the slave portion of latch 1304 havesubstantially the same timing characteristics, and which are notdependent on external clock propagation delays.

Previous techniques utilized to implement an error-detecting latchrequire manipulation of the propagation delay of disparate externalclock signals provided to the error-detecting latch using complexclock-tree and clock distribution analysis. Additional devices and nodecapacitance associated with multiple clock signals can increase theamount of power dissipated by the data processing device. The disclosederror-detecting latch 130 receives only one clock signal (signal CLK)and thus eliminates the need to precisely regulate the delay of multipleclock signals. This technique has the additional benefit that the timingcharacteristics of error detecting latch 130 are not dependent onmultiple external clock propagation delays. Thus, the timing propertiesof error detecting latch 130 can be characterized independent of itsinstantiations at a device.

FIG. 7 is a timing diagram 700 illustrating the operation of errordetecting latch 600 of FIG. 6 in accordance with a specific embodimentof the present disclosure. Timing diagram 700 includes a horizontal axisrepresenting time in picoseconds (pS), and a vertical axis representingvoltage in volts. Timing diagram 700 includes waveforms 702, 704, 706,708, 710, 712, 714, 716, and 718 representing signals at nodesassociated with devices included at error detecting latch 130 at FIG. 6.Waveform 702 corresponds to a clock signal at input node CLK andincludes transition 760, 766, and 786. Waveform 704 represents a signalat input node D and includes transitions 751 and 771 and transient pulse773. Waveform 706 represents a signal at node D1 based upon the signalat D1, e.g., a representation of the signal at input node D, andincludes transitions 753 and 775, and transient pulse 777. Waveform 708represents a signal at node D2 based on the signal at D, e.g., arepresentation of the signal at input node D, and includes transitions755 and 779, interval E 756, and transient pulse 781. Waveform 710represents a signal at node SN1 and includes transitions 757 and 783,and transient pulse 785. Waveform 712 represents a signal at node SN2and includes transitions 759 and 787. Waveform 714 represents a signalat node Q1 and includes transitions 761 and 789. Waveform 716 representsa signal at node Q and includes transition 763. Waveform 718 representsa signal at node ERROR and includes transition 791.

The setup time of latch 1302 is configured to be different than thesetup time of latch 1304 by configuring the propagation delay ofinverter 602 and inverter 632 to differ by a desired amount of time, E756. For example, inverter 632 can include three inverters connected inseries, while inverter 602 can include a single inverter. A low to hightransition 751 of data input signal D is received at the input ofinverter 602 and inverter 632, resulting in corresponding high to lowtransitions 753 and 755 at nodes D1 and D2 respectively. The propagationdelay of inverter 632 is configured to be greater than the propagationdelay of inverter 602 by an amount of time illustrated by an intervallabeled “E.” At the time that the nodes D1 and D2 transitions low, clocksignal CLK is negated so that the pass gate implemented by PMOStransistor 606 and NMOS transistor 604 and the pass gate implemented byPMOS transistor 636 and NMOS transistor 634 are both activated,resulting in transition 757 at node SN1 and transition 759 at node SN2.A subsequent low to high transition 760 at node CLK deactivates both ofthe pass gates associated with NMOS transistor 604 and NMOS transistor634 to latch identical logic values at latch 1302 and latch 1304. Thelow to high transition 760 causes the pass gate implemented by PMOStransistor 616 and NMOS transistor 614 and the pass gate implemented byPMOS transistor 646 and NMOS transistor 644 to be activated, and theinformation stored at latch 1302 and latch 1304 to be propagated to nodeQ1 (transition 761) and node Q (transition 763), respectively. Becausethe same information was successfully latched in latch 1302 and latch1304, signal ERROR is not asserted.

During the next clock cycle, a high to low transition 771 of data inputsignal D is received at the input of inverter 602 and inverter 632,resulting in corresponding high to low transitions 775 and 779 at nodesD1 and D2 respectively. At this time, clock signal CLK is negated sothat the pass gate implemented by PMOS transistor 606 and NMOStransistor 604 and the pass gate implemented by PMOS transistor 636 andNMOS transistor 634 are both activated, resulting in transition 783 atnode SN1 and transition 787 at node SN2. Shortly after transition 771 ofdata input signal D, a soft error at node D causes transient pulse 773.Transient pulse 773 is propagated through inverter 602 and inverter 632,resulting in transient pulse 777 at node D1 and transient pulse 781 atnode D2. The pass gate implemented by PMOS transistor 606 and NMOStransistor 604 is activated at the time the transient pulse occurs atinput D, and the signal received at node D1, including its subsequentrecovery to a logic-high level, is propagated to node SN1. Thelogic-high level is successfully stored at the master latch of latch1302 in response to transition 786 of signal CLK, resulting in a high tolow transition 789 at node Q1. However, because the signal provided tonodes D2 and SN2 are delayed with respect to nodes D1 and SN1, thesignal at node SN2 is unable to recover to a logic-high level before thepass gate implemented by PMOS transistor 636 and NMOS transistor 634 isdeactivated by the signal CLK. Thus, a logic-low level is latched at themaster latch of latch 1304, and signal Q remains at a logic-high level.Signal ERROR is asserted to indicate an error condition because latch1302 and latch 1304 have stored different values.

In an alternate embodiment, the timing requirements of latch 1302 andlatch 1304 can be adjusted by manipulating properties associated withother devices along their respective delay paths. For example,increasing the threshold voltage of NMOS transistor 604 and PMOStransistor 606 relative to the threshold voltage of NMOS transistor 634and PMOS transistor 636 changes the I/V characteristics of these devicesand thus modifies the switching characteristics of inverter 608 and 638,respectively, to introduce and effective delay. In another embodiment,the capacitance at storage node SN1 can be increased relative thecapacitance at storage node SN2 to increase the propagation delay ofdata from input D to node SN1 of the data path through latch 1302, andthereby reducing the setup time of the master latch. In yet anotherembodiment, the switching characteristics of inverter 608 or inverter638 can be manipulated by adding delay elements, adjusting transistordimensions, doping levels, or the like, to modify the timingrequirements of latch 1302 and latch 1304.

Note that not all of the activities or elements described above in thegeneral description are required, that a portion of a specific activityor device may not be required, and that one or more further activitiesmay be performed, or elements included, in addition to those described.Still further, the order in which the activities are listed are notnecessarily the order in which they are performed.

Also, the concepts have been described with reference to specificembodiments. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the present disclosure as set forth in the claims below.Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense, and all such modificationsare intended to be included within the scope of the present disclosure.For example, in an embodiment, error-detecting latch 130 can beimplemented using standard cells available in an existing standard celllibrary. Latch 1302 and latch 1304 can be selected from existingmaster-slave latches based on their timing characteristics and based onthe transition time of the corresponding data input signal.Error-detecting latch 600 described at FIG. 6 represents one example ofhow error-detecting latch 130 can be implemented. Latch 1302 and latch1304 can be implemented using another type of latch circuit thatprovides the disclosed timing characteristics. Furthermore, the termlatch is used broadly in the disclosure and is applicable to varioustypes of storage elements that store information based upon a clocksignal. Types of latches include level-sensitive latch, edge-triggeredlatch, or flip-flop such as a JK flip-flop or a D flip-flop.

An error detecting latch, such as error detecting latch 130, can includemore than two latches, and majority-voting logic can be used todetermine the value of data provided at the output of error detectinglatch 130 based on respective values stored at each latch. Signal ERRORis asserted if all latches included at error detecting latch 130 havenot stored the same value. Furthermore, three latches can be included aterror detecting latch 130 and each latch can include different setup andhold times relative to the other latches.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

1. A device comprising: a data input to receive a data signal; a clockinput to receive a clock signal to latch information based on the datasignal; a first signal path including the data input and a first latch,the first signal path having a first delay between the data input and afirst data node for a given transition at the data input; and a secondsignal path including the data input and a second latch, the secondsignal path including a first data node at a same location relative tothe second latch as the first data node of the first signal path islocated relative to the first latch, the second signal path having asecond delay between the data input and the first node of the secondsignal path for the given transition, the second delay beingsubstantially different that the first delay; wherein the first signalpath further comprises a first pass gate comprising a first currentelectrode coupled to receive information from the data input, and asecond current electrode coupled to provide the information to the firstlatch, the first pass gate having a third delay between the firstcurrent electrode and the second current electrode for the given signal;and wherein the second signal path further comprises a second pass gatecomprising a first current electrode coupled to receive information fromthe data input, and a second current electrode coupled to provideinformation to the second latch, the second pass gate having a fourthdelay between the first current electrode and the second currentelectrode for the given signal, the difference between the first delayand the second delay is substantially the same as the difference betweenthe third delay and the fourth delay.
 2. The device of claim 1 furthercomprising a data output coupled to the first latch to provide a latcheddata value.
 3. The device of claim 1 wherein the latched data value isbased on the first latch but not the second latch.
 4. The device ofclaim 3 further comprising an error output coupled to the first latchand to the second latch to provide an indicator that the latched datavalue is to be considered invalid.
 5. The device of claim 1 wherein thethird delay and the forth delay are determined based on respectiveelectrical characteristics of the first pass gate and the second passgate.
 6. The device of claim 1 wherein timing characteristics of asignal provided at the output of the device is not based on the firstdelay or the second delay.
 7. A method comprising: receiving a signaltransition at a data node of a latch module, the signal transitionreceived at substantially the same time at a first source/drain of afirst transistor and at a first source/drain of a second transistor;providing a first representation of the signal transition to a secondsource/drain of the first transistor at a first time; providing a secondrepresentation of the signal transition to a second source/drain of thesecond transistor at a second time; receiving, at a third time, aninitial portion of a clock transition at a gate of the first transistorto latch information at a first storage node of the latch module; andreceiving, at substantially the third time, the initial portion of theclock transition at a gate of the second transistor to latch informationat a second storage node of the latch module.
 8. The method of claim 7further comprising indicating an error condition based upon informationlatched at the first storage node and at the second storage node.
 9. Themethod of claim 7 wherein the first time and the second time aredetermined based on respective electrical characteristics of the firsttransistor and the second transistor.
 10. The method of claim 7 whereinthe first time and the second time are determined based on a respectivecapacitance at the second source/drain of the first transistor and atthe second source/drain of the second transistor.